Industrial automation refers to the use of control systems to independently operate and monitor a mechanised system of industrial processes. The industrial automation sector exhibited a huge growth over the last few years, with a global market of ˜150 billion U.S. Dollars by 2011, which is expected to grow beyond 200 billion by 2017.
Traditionally, wired communication served the industrial automation sector due its reliable dedicated infrastructure; however, at an exorbitant cost of installation and maintenance. Wireless solutions provide a low-cost alternative to wired solutions and therefore, increasingly gaining popularity for industrial automation applications.
Currently, wireless technologies are primarily used for monitoring and open-loop control applications at different layers of the automation pyramid. Open-loop control does not utilise any feedback. Accordingly, control messages are sent out but no response is returned to the controller. This is in contrast to closed-loop control, which includes feedback to the controller. This therefore requires bi-directional communication.
The use of wireless technologies for closed-loop control applications is constrained by the limitations of current solutions in terms of latency, reliability, and scalability. Moreover, the peculiarities of closed-loop control such as bi-directional information flow, cycle time, etc. create various challenges for protocol design.
Industrial automation is generally split into process and factory automation. Process automation involves manufacturing operations that convert highly variable raw materials into consistent quality finished goods. Process automation is a continuous process and involves analogue controllers (e.g. proportional-integral-derivative (PID) controllers). Typical applications of process automation include monitoring and control of fluids in steel, chemical, petroleum, and other similar industries.
On the other hand, factory automation deals with assembly of high quality engineered components into final product configurations. Factory automation is a discrete process and involves digital controllers (e.g. programmable logic controllers (PLCs)). Typical examples of factory automation include assembly line process for automobile, packaging, home appliances, and other similar industries.
The networking requirements for factory automation and process automation have some key differences. The former comprises star topology environments whereas the latter consists of mesh topologies. While a very high reliability of up to 99.999% (in terms of packet delivery ratio) is required for both, the latency requirements for factory automation are much more stringent compared to process automation. Typically, factory automation requires 2-10 ms latency (in terms of cycle time). However, process automation requires an end-to latency on the order of 20-30 ms (in terms of cycle time). Further, process automation requires high scalability, with support for up to 100-150 devices.
There is therefore a need for a novel wireless solution for closed-loop control operation in mesh-topology environments (e.g. process automation) wherein low latency (˜20-30 ms cycle time) and very high reliability (99.999% packet delivery ratio) is required along with high scalability (up to 100-150 devices).